1. Field of the Invention
The present invention relates to a variable resistor adapted to be used for a video game machine or the like.
2. Description of the Related Art
A conventional variable resistor will be described with reference to FIGS. 10 to 13. An insulated substrate 32 is housed in a case 31 comprising a synthetic resin form.
A fixed contact 33 having a pair of comb-shaped contacts formed at a certain interval on one side surface of the insulated substrate 32 as shown in FIGS. 11 and 13.
A fixed resistor 34 is attached to the other surface of the insulated substrate. As shown in FIG. 13, connection of the fixed contact 33 and the fixed resistor 34 is accomplished by connecting one of the contacts of the fixed contact 33 and a side of the fixed resistor with a connection line 35. The other contact of the fixed contact 33 is grounded with a connection line 36. The other end of the fixed resistor 34 is connected to a power supply terminal T1 via a connection line 37. An outgoing terminal T2 is connected to the connection line 35 via a connection line 38.
A pressure-sensitive member 39 is made of a disk-shaped pressure-sensitive conductive rubber. This pressure-sensitive member 39 is arranged to be spread over the pair of fixed contacts 33.
A buffer member 40 is made of a rubber material. The buffer member 40 is placed on the upper surface of the pressure-sensitive member 39 in a state in which it faces the fixed contact 33, and attached thereto by an adhesive or the like.
An operating member 41 comprising a synthetic resin form or the like is positioned on the upper surface of the buffer member 40 and attached in a state projecting from a hole 31a of the case 31.
Operation of the conventional variable resistor having the aforementioned configuration will now be described. When pressing the upper surface of the operating member 41, the pressure-sensitive member 39 is pressed via the buffer member 40 and deformed under the pressure to cause a change in resistance value at the portion of the pressure-sensitive member 39 thus pressed. The change in resistance value caused by a change in this pressing force is detected between the pair of comb-shaped contacts of the fixed contact 33.
Upon release of the pressing operation of the operating member 41, the pressure-sensitive member 39 and the buffer member 40 recover the original state thereof under the effect of their own elasticity, and at the same time, the operating member 41 as well recovers its original state.
The change characteristic of pressing force and electric resistance when using the pressure-sensitive member 39 is such that, as shown in FIG. 12, the resistance value steeply changes in the initial stage of pressing, exhibits a curved change in the middle stage that follows, and almost no change in the final stage, as represented by a change curve K2.
Because the pressure-sensitive member 39 is made of a pressure-sensitive conductive rubber, the characteristic (change curve) shows a large scattering, and in the manufacture of the pressure-sensitive member 39, furthermore, a scatter occurs in thickness, resulting in a serious scattering of characteristic (change curve).
Such a variable resistor is adapted to be used in an electric circuit diagram as shown in FIG. 13, incorporated in a game machine or the like.
In this circuit diagram, when a voltage is impressed between a terminal T1 and the connection line 36, an output voltage available between the fixed resistor 34 and the variable resistor based on the pressure-sensitive member 39 on the fixed contact 33 is taken out from a terminal T2.
When using such a variable resistor, for example, for speed operation of vehicle in a game machine, the resistance value steeply changes in the initial stage of pressing operation of the operating member 41, thus making it difficult to perform speed operation. In the latter stage of pressing operation, there is almost no change in resistance value. This causes the operator to feel an uncomfortable sense of being out of tune with the speed relative to the pressing operation.
When utilizing only the curved changing portion in the middle of the change curve K2, the slight change in resistance value during this course leads to a poorer operability.
In the conventional variable resistor, the use of the pressure-sensitive member 39 made of a pressure-sensitive conductive rubber causes a serious scattering of characteristic (change curve). Further, in the manufacture of the pressure-sensitive member 39, scattering of thickness poses a problem of a large scattering of the characteristic (change curve).
When using the variable resistor using a pressure-sensitive member 39, for example, for speed operation of a vehicle in a game machine, a steep change in resistance value in the initial stage of pressing operation of the operating member 41 makes it difficult to perform speed operation, and in the latter stage of pressing operation, the slightest change in resistance value causes a problem of a serious feeling of uncomfortability of being out of tune with the speed relative to the pressing operation.
When using only the curved changing portion in the middle of the change curve K2 of the pressure-sensitive member 39, the slightest change in resistance value in this middle stage leads to a problem of a poorer operability.
In this case, the pressure-sensitive member 39 is always in a state of preliminarily being pressed by the fixed contact 33. The pressure in this case is not constant under the effect of dispersion of size of parts and assembly, thus resulting in a serious scatter of output derived from the outgoing terminal T2 in the non-operating state. In addition, deterioration with time of elasticity of the pressure-sensitive member 39 leads to a problem of a shorter service life. Since it is necessary to use the fixed resistor 34 separately from the variable resistor and the fixed resistor 34 is attached and wired onto the insulated substrate 32, there is posed another problem of complicated operation and a higher cost.